1. Field of the Invention
The present invention relates to controls for torque converter lockup and/or bypass clutches. In particular, the present invention relates to a control for engaging a torque converter lockup clutch in a vehicular automated mechanical transmission system.
2. Description of the Prior Art
Automated mechanical transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,850,236; 5,406,861; 5,441,464; 5,487,004 and 5,509,867, the disclosures of which are incorporated herein by reference. Automated mechanical transmission systems having torque converters and torque converter lockup or bypass clutches are available under the "CEEMAT" trademark from EATON CORPORATION, assignee of this application. Transmission systems of this type may be seen by reference to U.S. Pat. Nos. 4,784,019; 4,850,861; 5,099,711 and 5,136,897, the disclosures of which are incorporated herein by reference.
In the past, automated mechanical transmission systems having torque converters and torque converter lockup clutches locked up the torque converter at a specific engine RPM, usually determined at least in part by vehicle speed, without any modulation of engine torque. While this tended to result in somewhat harsh lockup events, it was not unacceptable, as the vehicles using such systems in the past tended to be heavy-duty construction and/or off-road vehicles. Such control logic, however, is less than satisfactory for systems utilized in heavy-duty, over-the-road vehicles or coaches.